Fond of hiding away in closets and cupboards, Opal likes to jump out at unsuspecting family members at inopportune times: while her mother is bathing, as the cook is proudly carrying an elegant soup tureen out of the kitchen. From under the stairs, ``Then out leaps Opal like a frog, / To terrify the family dog.'' Opal annoys everyone--until they realize she is feeling left out with the arrival of a new baby. Though this is hardly a new theme, Knight's straightforward, rhyming text focuses on the fun, not the lesson to be learned. Estrada's loose, bouncy illustrations are just right for bringing to life Opal and her startling antics. Opal-enthusiasm bursts through these merry pictures--and sometimes right off the page. Every detail here helps tell the story: front endpapers of the house exterior depict busy inhabitants at every window while Opal looks forlornly out one of them; in the final endpapers Opal busily helps tend the baby, while everyone else is still at their previous pastimes. A sure child-pleaser. Ages 3-up. (Nov.)